1. Field of the Invention
This invention relates to an ink feeding rate control method for controlling an ink feeding rate for each area corresponding to an ink key of an ink feeder in a printing machine based on measurement information on detecting patches printed on prints. Further, the invention relates to a data correcting method for a printing machine for correcting data such as measurement information on detecting patches in order to control an ink feeding rate and/or a dampening water feeding rate.
2. Description of the Related Art
Such a printing machine includes ink feeders for adjusting the rates of feeding inks to ink rollers. Each ink feeder has a plurality of ink keys juxtaposed in a direction perpendicular to a direction for transporting printing paper in time of printing. The rate of feeding ink to the ink rollers is adjusted by varying the opening degree of each ink key. In this way, the rate of feeding ink ultimately to a printing plate is adjusted.
The printing plate has regions called detecting patches or control strips formed in positions corresponding to the respective ink keys. The opening degree of each ink key is adjusted by measuring, with a densitometer, the color density of a corresponding detecting patch actually printed on printing paper (see Japanese Unexamined Patent Publication No. 2002-355950, for example).
FIG. 11 is an explanatory view schematically showing detecting patches P1, P2, P3 and P4 printed on printing paper S acting as a print.
Each of areas E1, E2 and so on of the printing paper S corresponding to the respective ink keys of ink feeders has printed therein, for example, a detecting patch P1 corresponding to cyan ink, a detecting patch P2 corresponding to magenta ink, a detecting patch P3 corresponding to yellow ink, and a detecting patch P4 corresponding to black ink.
Specifically, as shown in FIG. 11, where a plurality of cyan images I are printed on the printing paper S, the area E1 has no images I in an area e1 aligned with the detecting patch P1 in the printing direction (i.e. a rectangular area having substantially the same width as the detecting patch and extending in the printing direction). On the other hand, the area E2 has a plurality of images I arranged in an area e2 aligned with the detecting patch P1 in the printing direction (i.e. a rectangular area having substantially the same width as the detecting patch and extending in the printing direction).
With such prints, cyan ink is little consumed in an image area of a printing plate corresponding to the area e1. The detecting patch P1 in the area E1 has a relatively high color density of cyan ink. Thus, the ink feeder is controlled to reduce the feeding rate of cyan ink for the area E1. Conversely, cyan ink is consumed in a relatively large quantity in an image area of the printing plate corresponding to the area e2. The detecting patch P1 in the area E2 has a relatively low color density of cyan ink. Thus, the ink feeder is controlled to increase the feeding rate of cyan ink for the area E2.
There can be a difference between an image area of areas e1, e2 and so on aligned with the detecting patches P1, P2, P3 and P4 in the printing direction (i.e. rectangular areas having substantially the same width as the detecting patches and extending in the printing direction) and an average image area of the areas E1, E2 and so on having these detecting patches P1, P2, P3 and P4 arranged therein. In such a case, the ink feeding rate cannot be controlled accurately. Such a drawback constitutes a serious problem particularly where each ink feeder of the printing machine has a small number of ink rollers with a low effect of ink distribution.